1. Field of the Invention
The invention disclosed in this specification relates to a motor drive device, a magnetic disk storage device and an electronic appliance that use the motor drive device.
2. Description of Related Art
Generally, in a hard disk drive used in various applications, the hard disk drive includes a function (a power off retract function) that operates a magnetic head automatically to an outside lamp mechanism further than an outermost circumference of a platter when a power supply voltage applied from host computer is abnormal. (e.g., power supply interruptions, instantaneous power failure, and so on)
Here, as an example of a conventional technology related to the above description, there is U.S. Pat. No. 6,188,192 B1 specification.
After the power supply applied from the host computer is cut off, during the above-mentioned power off retract, the power supply is continued to a voice coil motor and the like for driving the magnetic head by using a phase voltage generated during idling of a spindle motor (generally, 3-phase brushless DC motor) which keeps rotary drive of the platter so far. The power supply from the spindle motor to the voice coil motor need to be continued until an evacuation of the magnetic head is completed at least. Therefore it is important to reduce unnecessary energy loss.